1. Field of the Invention
This invention relates to a compact, integrated burner combining the concepts of premixing fuel and oxidant and indirect radiant heating.
2. Description of the Prior Art
Gas-fired infrared, or radiant, burners are of two general types: (1) direct, in which the gas is burnt on a porous solid, a screen, or some other similar device, and the infrared radiation is transmitted by the flame and/or glowing burner, or (2) indirect, in which hot combustion gas is used to heat up a secondary metal surface, which then emits infrared radiation. Generally, indirect burners are also designed such that combustion gas is kept separate from the area to be heated, protecting that area from potential exposure to pollutants and hazardous components in that gas. In cooking and heating applications, both types of burners are used.
Another important classification of burners is based upon the level of mixing of the inlet gases. When the fuel and oxidant are thoroughly mixed prior to introduction to the burner, the flame is known as premixed. Alternatively, when the fuel and oxidant are not thoroughly mixed prior to introduction to the burner, the flame is known as a diffusion flame. Diffusion flames typically have longer and larger flame regions, since the fuel and oxidant only get more intimately comingled, and more capable of igniting, as distance from the inlet increases. Partly for this reason, in diffusion flame applications with indirect radiant heating, the surface being heated is often a tube or plate that is physically separate from the burner assembly and the flame energy is transferred to the radiating surface rather far from the actual burner. On the other hand, in a premixed burner, the entering gas mixture is already capable of igniting completely. Premixed flames tend to burn cleaner and hotter, requiring less of the excess air that dilutes and cools the flame. The radiating surface can be located much closer to the flameholder than a burner using a diffusion flame.
Currently, indirect radiant burners used for space heaters and similar applications are only of the diffusion type, limiting the degree to which those appliances and devices may be made compact and space-saving. Therefore, a need exists to combine the indirect and premixed features of existing burners into a compact, integrated package suitable for space heaters or other applications where a large amount of radiant heat must be released and utilized in a relatively small space.
It is one object of this invention to provide a burner that combines indirect and premixed features of existing burners into a compact, integrated package suitable for space heaters and other applications where a large amount of radiant heat must be released and utilized in a relatively small space.
It is another object of this invention to provide a burner that heats the radiating surface faster and, if desired, to a higher temperature with less wasted volume for mixing.
It is another object of this invention to provide a burner that is particularly adaptable for removal of additional heat from the combusted gas downstream of the burner assembly.
It is a further object of this invention to provide a burner having a radiation plate formed by the combusted gas plenum, wherein a gas flow boundary also serves as a heat radiating surface.
It is another object of this invention to provide a burner which has great flexibility in the shape and size of the combustion region and the radiant surface.
It is yet another object of this invention to provide a burner which can be operated with the flame propagating either upwards or downwards.
A burner according to one preferred embodiment of this invention comprises a back plate, a flameholder plate and a radiation plate. The back plate preferably accepts at least one inlet for providing fuel and oxidant to a plenum of the burner. The plenum is preferably formed between the back plate and the flameholder plate.
The fuel and oxidant are preferably premixed and either blown or drawn through the flameholder plate. Premixing preferably occurs in the plenum through the action of turbulence, aided by one or more baffles positioned between the flameholder plate and the back plate. The resulting premixture is then fed through the flameholder plate.
Accordingly, the flameholder plate preferably further includes a plurality of ports formed in the flameholder plate downstream of the premixing baffles. The ports permit the premixture to enter a combustion chamber on an opposite side of the flameholder plate as the plenum.
The radiation plate is connected with respect to the flameholder plate and preferably forms a combustion chamber, such as a trough or depression, along which heat transfer to the radiating surface is preferably reasonably uniform. An ignitor preferably ignites the premixture to form a flame that extends from the flameholder plate and into the combustion chamber formed between the radiation plate and a bottom of the flameholder plate. The combustion chamber is preferably formed outwardly with respect to the flameholder plate and in a convex configuration of varying depth.
An outlet is preferably formed in a deep portion of the combustion chamber and is connected to a tube that is connected to a downstream tube or is mateable with a corresponding tube end of a downstream portion, such as a flue vent or a convective heat exchanger, of the device. Air flow can be created through the outlet by either a forced air blower or an induction fan.